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SubjectRe: [PATCH v3 02/12] iommu: Add iommu_split_block interface
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On 4/13/21 4:54 PM, Keqian Zhu wrote:
> Block(largepage) mapping is not a proper granule for dirty log tracking.
> Take an extreme example, if DMA writes one byte, under 1G mapping, the
> dirty amount reported is 1G, but under 4K mapping, the dirty amount is
> just 4K.
>
> This adds a new interface named iommu_split_block in IOMMU base layer.
> A specific IOMMU driver can invoke it during start dirty log. If so, the
> driver also need to realize the split_block iommu ops.
>
> We flush all iotlbs after the whole procedure is completed to ease the
> pressure of IOMMU, as we will hanle a huge range of mapping in general.
>
> Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com>
> Signed-off-by: Kunkun Jiang <jiangkunkun@huawei.com>
> ---
> drivers/iommu/iommu.c | 41 +++++++++++++++++++++++++++++++++++++++++
> include/linux/iommu.h | 11 +++++++++++
> 2 files changed, 52 insertions(+)
>
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 667b2d6d2fc0..bb413a927870 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -2721,6 +2721,47 @@ int iommu_domain_set_attr(struct iommu_domain *domain,
> }
> EXPORT_SYMBOL_GPL(iommu_domain_set_attr);
>
> +int iommu_split_block(struct iommu_domain *domain, unsigned long iova,
> + size_t size)
> +{
> + const struct iommu_ops *ops = domain->ops;
> + unsigned int min_pagesz;
> + size_t pgsize;
> + bool flush = false;
> + int ret = 0;
> +
> + if (unlikely(!ops || !ops->split_block))
> + return -ENODEV;
> +
> + min_pagesz = 1 << __ffs(domain->pgsize_bitmap);
> + if (!IS_ALIGNED(iova | size, min_pagesz)) {
> + pr_err("unaligned: iova 0x%lx size 0x%zx min_pagesz 0x%x\n",
> + iova, size, min_pagesz);
> + return -EINVAL;
> + }
> +
> + while (size) {
> + flush = true;
> +
> + pgsize = iommu_pgsize(domain, iova, size);
> +
> + ret = ops->split_block(domain, iova, pgsize);
> + if (ret)
> + break;
> +
> + pr_debug("split handled: iova 0x%lx size 0x%zx\n", iova, pgsize);
> +
> + iova += pgsize;
> + size -= pgsize;
> + }
> +
> + if (flush)
> + iommu_flush_iotlb_all(domain);
> +
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(iommu_split_block);

Do you really have any consumers of this interface other than the dirty
bit tracking? If not, I don't suggest to make this as a generic IOMMU
interface.

There is an implicit requirement for such interfaces. The
iommu_map/unmap(iova, size) shouldn't be called at the same time.
Currently there's no such sanity check in the iommu core. A poorly
written driver could mess up the kernel by misusing this interface.

This also applies to iommu_merge_page().

Best regards,
baolu

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